The present invention relates to high voltage motor controllers, and more particularly to a novel safety feature comprising a lamp which is energized to warn of the presence of high voltage within the controller cabinet.
Motor control centers of the high voltage type are ordinarily provided with large, heavy contactors for opening and closing a load circuit, specifically for connecting and disconnecting motors to sources of high voltage. Owing to the size and weight of the contactors utilized for this purpose, the contactors are ordinarily mounted in a withdrawable carriage assembly which is fitted with wheels or rails for ease of removal from within the controller cabinet so that the contactor can be inspected, serviced or replaced with relative ease.
Owing to the high voltages and currents which the contactor is expected to manage considerable attention has been given to the construction of the fixed connections within the cabinet, and the mating connectors on the contactor assembly which engage them. Typically such connections comprise a rigid metal element termed a "stab," and a set of spring-loaded "fingers" which are forced over and tightly grip the stab. Engagement of the contactor assembly with the stabs not only supplies high voltage electricity to the main contactor elements, but also energizes a transformer which in turn supplies lower-voltage power to various control system elements, which are ordinarily mounted upon the contactor carriage assembly.
Because of the heavy, rugged construction of the main contacts, motor controllers are commonly provided with racking mechanisms which engage the contactor carriage assembly and forces it tightly into engagement with the bus bar stabs, completing a circuit from the line power supply to the contactor and from the contactor to the controlled load.
Owing to the high voltage which is then present upon the contactor, it is necessary to prevent ready access to the contactor. This end is ordinarily accomplished by a series of mechanical interlocks which ensure that the door to the contactor cubicle cannot be opened unless the contactor assembly is disengaged, or unracked. Such interlock arrangements are ordinarily provided as part of the racking mechanism, so that when the mechanism is in the "unracked" position, the door can be opened and access gained to the contactor and a technician may safely assume that the contactor is completely deenergized.
In addition to the release of the compartment door as an indication of deenergization, some manufacturers provide other indications that the contactor assembly is unracked. Typically the racking handle is labeled with "On" and "Off" legends signifying racked and unracked positions of the contactor. Still other manufacturers provide mechanical flags or the like which are directly operated by the position of the contactor assembly or the racking mechanism. In all of these instances, however, what is actually signified is the position of the control mechanism, or of the contactor carriage; the actual presence of electrical power upon the contactor assembly is not directly monitored.
The underlying assumption in the various interlock or alarm systems which have historically been used is that the movement or position of certain mechanical elements will necessarily result in the deenergization of the contactor assembly. However the present inventors have noted that many, if not most, serious accidents involving high voltage contactor assemblies result from persons gaining access to the contactor compartment while the contactor assembly is still energized. Such access may occur inadvertently through ignorance, or by deliberately defeating the various mechanical interlocks which have been provided as safety measures. Accordingly, it will be seen that it would be highly desirable to provide a high voltage motor control center with a highly visible indication of presence of electrical power in a high voltage contactor assembly, regardless of status or position of various mechanical elements within its cabinet.
It is therefore an object of the present invention to provide an improved warning system for a high voltage contactor assembly.
Yet another object is to provide highly visible warning means which will indicate the electrical state of a high voltage contactor assembly.
Yet another object is to provide an improved warning mechanism which cannot be defeated by the destruction or overpowering of a racking mechanism.